The present invention relates to improvements in clutches in general, and more particularly to improvements in friction disc arrangements of the type disclosed, for example, in U.S. Pat. No. 3,203,205 granted Aug. 31, 1965 to Geibel et al.
The clutch disc arrangement which is disclosed by Geibel et al. comprises two lateral disc-shaped guides which rotate with the radially outwardly extending mounting flange of a hub and flank a clutch disc which carries the customary friction coatings. The clutch disc has limited freedom of angular movement relative to the hub and/or vice versa. For the sake of simplicity, reference will be made to rotation of the clutch disc relative to the hub with the understanding, however, that the situation is the same if the hub turns relative to the clutch disc and/or if the clutch disc and the hub turn in the opposite directions or in the same direction but at different speeds. At least certain stages of angular movement of the clutch disc relative to the hub are opposed by suitable energy storing devices in the form of coil springs which are inserted into windows or openings provided therefor in the clutch disc and in at least one of the disc-shaped guides on the hub. An advantage of clutch disc arrangements of the type disclosed by Geibel et al. is that they can transmit pronounced torque even if their dimensions are relatively small.
It is often desirable or necessary to transmit a pronounced or maximum torque only after a certain angular displacement of the clutch disc relative to the hub (i.e., the resistance to initial angular displacement of the clutch disc relative to the hub should be less than during the next-following stage or stages of angular movement of the clutch disc). As proposed in German Pat. No. 24 36 288 granted Oct. 6, 1977 to the assignee of the present application, this can be achieved by installing a so-called load friction unit between one of the guides (which rotate with the hub) and the clutch disc. The load friction unit which is disclosed in the German patent comprises at least one friction disc, a friction pad and energy storing springs installed between the guides and the friction disc to oppose at least certain stages of angular movement of the clutch disc relative to the guides. In this manner, one can ensure that, when the clutch disc leaves a neutral angular position, the initial stage of its angular movement relative to the hub is opposed by a soft or smooth damping action whereas the load friction unit becomes effective only when the angular displacement of the clutch disc relative to the hub progresses beyond the aforementioned initial stage. The damping action during such second or further stage or stages of angular displacement of the clutch disc relative to the hub is much more pronounced than during the initial stage or stages.